Alloy



Patented Nov. 8, 1938 UNITED STA'TES PATENT orries No Drawing.Application December 5, 1936,

Serial No. 114,370

2 Claims.

The present invention relates to a ferrous base alloy containingmolybdenum and boron as well as certain other alloy elements.

The object of the present invention is to pro- 5 vide an alloy which isentirely or substantially free from carbon and which has a combinationof advantageous physical properties and characteristics rendering-itparticularly valuable for use as metal cutting tools.

The type of alloy tool steel, usually classified as high speedsteelwhich has heretofore been in general use contains tungsten as theprincipal alloy element; the'standard 18-4-1 high speed steel beingsubstantially an alloy of iron with 8% tungsten, 4% chromium, 1%vanadium,

" 0.50% to 0.75% carbon and minor percentages of manganese and silicon.Various modifications have been proposed, such as steels containingapproximately four times as much molybdenum as tungsten, e. g., from 6%to 8% molybdenum and from l.5% to 2.5% tungsten; and steels containingfrom 6% to 12% molybdenum without tungsten.

All of the previously known high speed steels,

irrespective of whether they contain tungsten or molybdenum as theprincipal alloy element, de-

pend upon the presence of an appreciable amount of carbon to impart thedegree of hardness necessary for metal cutting tools. An examination ofany of the previously known types of high speed steel discloses grainsor. particles of an excess constituent comprising a complex compound ofcarbon, tungstenand iron, or carbon, molybdenum and iron, as the casemay be. This constituent is commonly designated as the carbidesegregate.

. It is well known that a minimum carbon content of 0.50% is necessaryfor the development of the requisite hardness and cutting efficiency inhigh speed steel; the usual carbon content of such steel being from0.60% to 0.70%.

I have discovered that by combining appreciable amounts of molybdenum,boron, chromium and vanadium in a ferrous alloy entirely free fromcarbon that I can produce a composition which has a cutting eiliciencysuperior to previously known high speed steels containing appreciablepercentages of carbon. Furthermore, 50 by reason of the freedom fromcarbon the alloy of the present invention is amenable to a method ofthermal treatment which is markedly difierent from that required forheretofore known tool steels. By means of such thermal treatment 55hardness and other physical properties and characteristics determiningcutting eillciency can be accurately regulated over a wide range.

The essential components of the alloy of my present invention aremolybdenum, boron, chromium, vanadium and iron. Manganese and sili- 5con are usually present in minor amounts. Phosphorous and sulphur, aswell as certain other elements commonly found in alloy steels, areusually present in ineffective amounts in the nature of incidentalimpurities. 10

The alloy of the present invention comprises molybdenum 6% to 15%, boron0.30% to 2.25%,

chromium 1% to 5%, vanadium 0.70% to 4% and the remainder principallyiron. Manganese and silicon will usually be present in amounts not 15exceeding approximately manganese 1.10% and silicon 1.20%.

I prefer to have the alloy entirely free from carbon as when thiselement is absent the composition is not only more amenable to thermal20 treatment but, in general, has greater cutting efliciency. However,by reason of the fact that certain of the materials used in thepreparation of the alloy frequently contain varying amounts of carbon Ihave found that when my alloy is 25 manufactured under ordinarycommercial conditions it will frequently contain from about 0.03% to0.06% carbon in the nature of an 1 incidental impurity. I have foundthat such incidental carbon can be present in an amount 30 as highasapproximately 0.10% without materially decreasing the valuable physicalcharacteristics possessed by the carbon free alloy.

The presence of 0.45% or more carbon in high speed steels containingtungsten or molybdenum 35 as the principal alloy elements results in theformation of the carbide constituent or segregate referred tohereinabove. A relatively large portion of such constituent occurring incast ingots is in comparatively massive form, which can be 40 reduced insize and distributed throughout the steel only by mechanical working.Only the smallest particles of the carbide constituent can be dissolvedin the matrix by means of heating. Consequently, a relatively largeproportion of the primary carbide constituent persists through all ofthe thermal treatments to which such steels are subjected. Therefore,the regulation of particle size and distribution of a major portion ofthe complex carbide constituent forming the segregate is entirelydependent upon mechanical working. This does not provide a satisfactorymethod of control of the physical structure of the aggregate.

I have previously proposed the use of boron as principal alloy element.I have found that such bore-carbide compounds are extremely hard andbrittle and that relatively coarse particles of this constituent cannotbe appreciably fragmented by mechanical working without rupturing thesteel.

I have also discovered that such bore-carbide constituents are onlypartially dissolved in the matrix by thermal treatment. It will beapparent, therefore, that the presence of an appreciable proportion ofsuch complex boro-carbides produces a steel in which the particle sizeand dissemination of the hard constituent cannot be closely regulated bythermal treatment.

' In the alloy of the present invention the segregate of the caststructure appears to be essentially a complex compound of boron,molybdenum and iron. This segregate can be more or less readilyfragmented by mechanical working, or it can be largely or entirelydissolved in the matrix by heating the cast aggregate.

Examples of alloys which I have found particularly useful for metalcutting tools contained molybdenum 9.25%, boron 0.85%, chromium 3.80%,vanadium 1.75%,' manganese 0.60%, silicon 0.40% and the balanceprincipally iron; molybdenum 11%, boron 0.93%, chromium 4%, vanadium 2%,manganese 0.55%, silicon 0.55%, carbon 0.04% and the balance principallyiron.

I have found that the hardness and other physical properties andcharacteristics of the alloy of the present invention can be accuratelycontrolled by means of suitable thermal treatment. As an illustration,one satisfactory method consists essentially of heating an aggregate ofthe alloy to a temperature in excess of 1000 C. maintaining theaggregate at this temperature for a sufficient period of time todissolve an appreciable proportion of the molybdenum-ironboron compoundin the matrix; quenching the aggregate to substantially retain the solidsolution; subsequently heating the aggregate to a temperaturesubstantially lower than that at which the solid solution was formed fora suiflcient period of time to produce precipitation ofmolybdenum-iron-boride particles from the solid solution. I have foundthat in carrying out the primary heating for effecting solid solution itis not necessary to dissolve all of the molybdenumiron-borldeconstituent in the matrix. After the alloy has been quenched from theprimary heating temperature it will usually have a hardness ofapproximately Rockwell C compared to a hardness of from to 69 Rockwell Cwhich can be developed by precipitation of the boron containingconstituent during the secondary heating. It will beapparent that byregulating the temperatures and periods of heating the ratio ofprecipitated boron compound to matrix constituent, or to primary boroncompound may be ac: curately controlled. The precipitated boron compoundis uniformly disseminated throughout the aggregate.

I have found that the boron containing constituent of the present alloyis not only extremely hard, but is relatively strong. The presence ofboron imparts high impact strength to the al- 10y, particularly attemperatures generated in the tip of a metal cutting tool. Such boroncontaining compounds are also highly resistant to oxidation at suchtemperatures, and consequently the injurious effect of decarburization,which occurs in carbon containing tools, is entirely eliminated.

Although the greatest scope of usefulness for this alloy appears to bein cast or wrought forms as cutting tools, I have found that it may beutilized for many other industrial applications such as forming dies,wearing parts, etc.

I claim:

1. An alloy containing molybdenum 6% to 15%, boron 0.30% to 2.25%,chromium 1% to 5%, vanadium 0.70% to 4%, manganese not exceedingapproximately 1.10%, silicon not exceeding approximately 1.20% and theremainder iron.

2. An alloy containing molybdenum 6% to 15 boron 0.30% to 2.25%,chromium 1% to 5%, vanadium 0.70% to 4%, carbon not exceedingapproximately 0.10%, manganese not exceeding approximately 1.10%,silicon not exceeding approximately 1.20% and the remainder iron.

ANTHONY G. DI: GOLYER.

